GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC C Sierra - 2WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 263-NP1 🢒 Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode

Circuit Description

The transfer case motor is a bi-directional, permanent magnet, DC motor. When energized through motor control A or motor control B, the ground is provided by the opposing motor control circuit and then grounded through the transfer case shift control module ground circuit. The motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the transfer case between the ranges of 4HI, 2HI, Neutral (N) and 4LO.

If motor control A and B circuits are shorted together, or a motor control driver is damaged in the transfer case shift control module, the transfer case shift control module goes into a shift block mode. The transfer case module also goes into shift block mode if there is a mechanical concern, causing the shift lever detent shaft to bind, or if the transfer case shift control module is not seeing a signal from the park/neutral position (PNP) switch. The shift block mode causes the mode indicator to flash for a period of time when another mode is selected. After that period of time has ended, the indicator reverts back to the previous mode selection.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step helps to determine if the transfer case shift control module has the ability to command the encoder motor.

    2.

  2. This step determines if motor control A and motor control B circuits being shorted together is causing a shift block.

    3.

  3. This step determines if the motor control A and motor control B circuits are shorted together within the module.

    4.

  4. This step determines if a binding shift lever detent shaft is causing a shift block.

    5.

  5. This step has the transfer case removed and repaired.

    6.

  6. This step determines if the PNP switch is sending the correct range signal.

    7.

  7. This step replaces the transfer case shift control module.

Step

Action

Value

Yes

No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check - Transfer Case?

--

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

  1. Turn the ignition ON, with the engine OFF.
  2. Install a scan tool.
  3. Go to ATC Data List on the scan tool and observe motor A and B current.
  4. Using the mode switch in the instrument panel, select the different modes.

Does the scan tool indicate an amperage draw from the motor?

--

Go to Step 3

Go to Step 7

3

  1. Turn the ignition OFF.
  2. Disconnect the transfer case shift control module and the encoder motor.
  3. With a DMM, check to see if motor control A and motor control B are shorted together. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 4

4

  1. Connect the transfer case shift control module.
  2. With a DMM, check motor control A and motor Control B circuits for being shorted together. Refer to Circuit Testing in Wiring Systems.

Does the DMM indicate a resistance less than the specified value?

100 ohms

Go to Step 8

Go to Step 5

5

Remove the encoder motor and check to see if the shift lever detent shaft is binding. Refer to Transfer Case Encoder Motor Replacement .

Is the shift lever detent shaft binding?

--

Go to Step 6

Go to Step 9

6

Remove the transfer case and repair. Refer to Transfer Case Assembly Replacement .

Did you complete the repair?

--

Go to Step 10

--

7

Check the instrument panel to see if the correct transmission range is being displayed.

Is the correct range being displayed?

--

Go to Step 8

Go to Diagnostic System Check - Automatic Transmission in Automatic Transmission 4L60-E/4L65-E or Diagnostic System Check - Automatic Transmission 4L80-E/4L85-E

8

Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement and Transfer Case Shift Control Module Reprogramming .

Did you complete the repair?

--

Go to Step 10

--

9

Replace the encoder motor. Refer to Transfer Case Encoder Motor Replacement .

Did you complete the repair?

--

Go to Step 10

--

10
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for allowing the symptom to occur.

Does the symptom still occur?

--

Go to Step 2

System OK